N-methyl-D-aspartate (NMDA) receptors are involved in various forms of synaptic plasticity in the central nervous system, including learning, memory, and experience-dependent synaptic modifications. Excessive activation of NMDA receptors may be involved in ischemic brain damage, and in the etiology of some forms of epilepsy, and chronic neurodegenerative diseases such as Alzheimer's disease, Parkinson's disease, and dementias that occur after infection with human immunodeficiency virus. Antagonists or modulators of NMDA receptors may be clinically useful for the treatment of some of these pathologies. The NMDA receptor/ion channel complex contains a number of specific recognition sites for endogenous ligands, including binding sites for glutamate, glycine, Mg++, Zn++, and polyamines. The long-term objectives of the proposed studies are to investigate the regulation of NMDA receptors and the role of polyamines in modulating excitatory synaptic transmission and synaptic plasticity mediated by NMDA receptors. The specific aims of the proposed research are to investigate the regulation of NMDA receptors and the role of polyamines in modulating excitatory synaptic transmission and synaptic plasticity mediated by NMDA receptors. The specific aims of the proposed research are to investigate the acute and chronic regulation of the densities and properties of NMDA receptors in cultured neurons and in the developing rat brain, and to study the release of polyamines from cultured neurons and brain slices. Using radioligand binding assays with [125I]I-MK-801, an open-channel blocker of the NMDA receptor, the densities and properties of NMDA receptors will be determined in membranes prepared from cultured cortical neurons after exposure to modulators that act at distinct sites on the NMDA receptor complex. Cells will be treated with antagonists acting at the binding sites for glutamate and glycine, with open-channel blockers, with elevated concentrations of divalent cations, with agonists, antagonists, and inverse agonists at the polyamine recognition site, and with inhibitors of the synthesis, metabolism, and uptake of polyamines. Changes in the densities and properties of NMDA receptors will be investigated during postnatal development of the rat brain and over time in cultured neurons. The sensitivity of the receptors to polyamines and to modulators acting at other sites on the receptor complex will be investigated. Experiments will be carried out to identify the factors responsible for developmental changes in the properties of the NMDA receptor. Studies of the uptake, localization, and release of polyamines in cultured neurons and glial cells will also be carried out. Release of polyamines will be measured after preloading cells with radiolabeled polyamines or their metabolic precursors. Release of endogenous polyamines will be determined by derivitization, HPLC separation, and fluorescence detection. The characteristics and ionic-dependence of the uptake and release of polyamines will be investigated. The proposed research will provide information concerning the biochemical and cellular sequelae of treatment with modulators of NMDA receptors and the role of polyamines in modulating excitatory synaptic transmission. This work may lead to a better understanding of the role of NMDA receptors and polyamines in normal and abnormal brain function, and may have implications for the design and use of pharmaceuticals targeted toward the NMDA receptor.